A pacemaker is an implantable cardiac stimulation device for implant within a patient that analyzes an intracardiac electrogram (IEGM) to detect various arrhythmias, such as an abnormally slow heart rate (bradycardia) or an abnormally fast heart rate (tachycardia), and then to selectively deliver electrical pacing pulses to the heart in an effort to remedy the arrhythmias. An implantable cardioverter-defibrillator (ICD) additionally or alternatively detects atrial fibrillation (AF) or ventricular fibrillation (VF) and delivers electrical shocks to terminate fibrillation. For many patients, particularly those with congestive heart failure (CHF), it is desirable to identify a set of control parameters for controlling the operation of the pacemaker or ICD that will optimize cardiac performance (also referred to as hemodynamic performance). Cardiac performance is a measure of the overall effectiveness of the cardiac system of a patient and is typically represented in terms of stroke volume or cardiac output. Stroke volume is the amount of blood ejected from the left ventricle during systole in the forward direction. Cardiac output is the volume of blood pumped by the left ventricle per minute (i.e. stroke volume multiplied by the current heart rate of the patient).
One particularly useful control parameter for optimizing cardiac performance is the atrioventricular (A-V) pacing delay, which for dual-chamber devices specifies the time delay between a paced or sensed atrial event and a paced ventricular event. Another useful control parameter is the inter-ventricular pacing delay (V-V), which for biventricular pacing devices specifies the time delay between a paced or sensed right ventricular (RV) event and a paced left ventricular (LV) event. However, a wide variety of other parameters also affect overall cardiac performance. Numerous techniques have been developed for optimizing these and other parameters so as to improve cardiac performance. See, for example, U.S. patent application Ser. No. 11/366,930, of Muller et al., entitled “System and Method for Determining Atrioventricular Pacing Delay Based on Atrial Repolarization,” filed Mar. 1, 2006; U.S. patent application Ser. No. 10/928,586, of Bruhns et al., entitled “System and Method for Determining Optimal Atrioventricular Delay based on Intrinsic Conduction Delays”, filed Aug. 27, 2004; U.S. patent application Ser. No. 11/231,081, of Turcott, entitled “System and Method for Rapid Optimization of Control Parameters of an Implantable Cardiac Stimulation Device”, filed Sep. 19, 2005; and U.S. patent application Ser. No. 11/199,619, of Gil et al., entitled “System and Method for Determining Preferred Atrioventricular Pacing Delay Values based on Intracardiac Electrogram Signals”, filed Aug. 8, 2005.
Although an improvement in cardiac performance is often the goal, pacing therapy may alternatively be delivered to achieve other goals or to obtain other benefits. For example, for a patient suffering from high blood pressure, pacing therapy may be delivered so as to decrease blood pressure. If a patient is at risk of certain arrhythmias, pacing therapy may be tailored so as to decrease the risk of the arrhythmia. In one specific example, wherein a patient is subject to atrial tachyarrhythmias, dynamic atrial overdrive (DAO) pacing may be delivered so as to reduce the risk of such arrhythmias. In still other examples, pacing therapy is delivered so as to reduce the risk of VF. As can be appreciated, a wide variety of pacing parameters may be selectively adjusted so as to achieve a wide variety of goals. Hence, stated generally, pacing parameters are preferably optimized to enhance overall “pacing efficacy,” where the efficacy of pacing is evaluated with respect to the particular goal of the pacing regime. Numerous techniques have been previously developed for use by implantable medical devices to automatically adjust pacing parameters so as to improve overall pacing efficacy within the context of specific pacing regimes, such as the techniques of the patent applications listed above.
Heretofore, however, it does not appear that many techniques have been developed specifically for evaluating and optimizing the contribution of particular chambers to pacing efficacy. That is, predecessor techniques generally seek to determine pacing parameters that will improve overall pacing efficacy without regard to the specific contribution provided by particular heart chambers, such as just the right atrial (RA) contribution or just the LV contribution. By evaluating the contribution of particular chambers to pacing efficacy, the device can provide diagnostic information from which the physician can gain considerable insight into the health of those chambers. Moreover, an evaluation of the contribution of particular chambers to pacing efficacy can be exploited by the device itself to enhance or optimize the contribution of those chambers. In many cases, by optimizing the contribution of particular chambers to pacing efficacy, the device can thereby improve overall pacing efficacy so as to, for example, improve overall cardiac performance. Accordingly, it would be desirable to provide techniques for evaluating and optimizing the contribution to pacing efficacy provided by particular heart chambers. It is to this end that the invention is primarily directed.